The food processor, such as the soymilk machine, juicer/extractor, blender, etc, is an important category of household appliances. In recent decades, such food processors become popular in global market and loved by customers in China due to its convenience, speed and compatibility with the Chinese food. The core technology underlying the conventional soymilk machine, juicer, blender and other similar automatic food processors is of three major types as described below:
1. The food material is broken up by high speed rotation of metal blades. Conventional soymilk machines and food processors mostly belong to this type.
2. The food material is processed into small filaments or pieces by relative motion between the food material and a metal scraper which has numerous shaving holes (serves as small scraping blades) on the surface. The juice and residues are then separated by centrifugal force. The example is the scraper type juicer.3. The food material is pushed into a small chamber by a screw rod and extruded through a metal mesh filter placed at opposing end of the chamber. Alternatively, the food material can be cut into small pieces by a set of blades which moves relative to each other for cutting the food material into small pieces and extracting the juice. The examples are screw rod type juicer and meat grinder.
The food processors of the first and second types have following drawbacks:
1. Metal blades may become rusted and blunt after repeated use.
2. Processed food material may stick to metal blades due to the heat generated on the metal blades during operation, making them difficult to clean. This is particularly troublesome for the soymilk machine with a heater as the food material is more easily sticking to the metal blades upon being heated.3. Metal blades may become contaminated and produce abnormal odors due to bacteria growth in micro-pores on the surface of the metal blades, which can affect the flavor of the processed food material, affect food color due to chemical reaction upon contacting with the food material such as fruits, or even is detrimental to health due to the small amount of heavy metal elements released from the metal blades during blending and grinding operations.
The conventional automatic soymilk machines as described above are not really the same as the traditional way of making soymilk. In the traditional way, the soy beans are grinded manually using a stone mill. The stone mill can have various types such as wet mill, dry mill, oil mill or paste mill, etc. Among them, the wet mill is a traditional tool specifically for making soymilk. The soy beans to be processed are put between a pair of milling plates (including an upper plate 36 and a lower plate 37, see FIG. 1) after being soaked in water. Opposing surfaces of the upper and lower plates 36 and 37 both have milling teeth 38 in peripheral regions along radial directions. The length of milling teeth 38 of the upper plate 36 smaller than that of the milling teeth of the lower plate 36. The milling teeth 38 can have an arrangement of eight divisions each with eight teeth (as shown in FIG. 1). Alternatively, the milling teeth 38 can have other arrangements such as ten divisions each with four teeth or ten divisions each with six teeth depending on the need of the specific circumstance. Water is added through the feeding inlet while the milling plates rotate, and the soy beans are pressed by the pair of milling plates and grinded by the milling teeth due to relative movement of the two milling plates. The process then yields soymilk. During such milling process, the soy beans are under a variety of actions such as crushing, pressing, tempering, rubbing, twisting and grinding, which makes soymilk rich in flavor and taste good.
It has been found that the low rotation speed of the stone mill is directly related to the richness in flavor of the soymilk produced in the traditional way. Traditional manpowered stone mill operates at a rotational speed of 4-7 rpm. During such low speed process, the protein in the soymilk is sufficiently exposed to the air and thus fully oxidized. The slower the rotation speed is, the richer the flavor of the soymilk would be. This is why the soymilk made by the traditional stone mill has rich aroma and flavor. In addition, the soymilk is filtered with cotton cloth to remove finer residual powders particles and is thus tender and smooth with great taste.
In comparison, most of conventional existing soymilk machines employ a blending process of the first type mentioned above, in which the soy beans are broken or beat up into small pieces, and they are blended and heated at the same time. As such, the traditional milling process is replaced by a simple pulverization and crushing process in such soymilk machines. Therefore a large amount of bean residual powders are kept in the soymilk. In addition, the rotational speed of the blades in the soymilk machine (over 10,000 rpm) is much greater than the rotational speed of a traditional stone mill, which can destroy some nutrients in the soymilk and thus lower the extraction rate of bean nutrients. The soymilk made by such soymilk machine is drastically different from the soymilk made by the traditional stone mill in terms of flavor, taste and nutrient level. In other words, the traditional stone mill produces better soymilk. Furthermore, the soymilk machine of the first type does not have a separation step for separating soymilk and residuals. The resulting soymilk contains both the milk and residuals, which not only affect taste but also affect absorption of nutrient ingredients by the human body. In addition, those conventional soymilk machines vibrate due to the high speed rotation, which in turn generates unpleasant noises.
The soymilk machine of the third type is rare, but Chinese patent application No. 200780001269.X entitled “JUICER” discloses a soymilk/juice machine of such type. As shown in FIGS. 1 and 2 therein (corresponding to FIGS. 2 and 3 in the present application, respectively), the juice machine includes a screw rod 200 and a meshed can 300, installed vertically in a concentric nesting manner. The height of the screw thread on the surface of the screw rods 200 decreases from top to bottom. There is a grinding plate disposed on the inner surface of the meshed can 300. The food material enters the gap between the meshed can and the threads of the screw rod from above. The food material in the gap is then squeezed and crushed by rotating the screw rod and the juice generated during the process flows through the meshed can via the mesh filters disposed at the upper and lower positions (which are straining mesh 320 and squeezing mesh 330 respectively) and is discharged from the juice outlet, and the residuals are discharged via residual outlet 570.
The juicer described as above has following drawbacks: since the screw rod is shaped like a loom shuttle, with two smaller ends and a bigger midsection, which makes it impossible to provide a grinding section at the lower end below the middle pulverization section. The gap between the screw rod and meshed can of a profile like “K.” has an upper section f1 for guiding and breaking, which has a greater gap size. The middle section f2 is for pulverization with a smaller gap, and a lower section f3 for juice/residual separation with a slightly increased gap. As the outer surface of the screw rod and the inner surface of the meshed can assume a “K” profile, the device lacks a grinding section to perform a grinding process like the traditional stone mill which requires two generally parallel opposing grinding surfaces. The gap in section f1 is decreased gradually from top to bottom and reaches a minimum at the pulverization section f2. The food material goes through the stages of guiding, breaking, pulverization and eventually enters into a juice/residual separation section. The juicer processes the food material by squeezing and crushing, unlike the grinding process in the conventional manpowered milling. Therefore, although the screw rod rotates slowly, the flavor and taste of the soymilk is still drastically worse than the soymilk made by the traditional stone mill approach due to the lack of the grinding process. In addition, since the food material is not grinded, the food material has bigger particle sizes, which can readily get stuck in the filter mesh of the mesh can and need to be brushed off into the milk by the rotating brush 400. Otherwise, the filter mesh will be blocked, affecting soymilk throughput. This will also increase the powder contents of the soymilk and affect the tenderness and smoothness of the soymilk.